Strange thing....Ive been bleeding for 12 days straight, it's not heavy barely filling one side of my tamp. Af was late…

Strange thing....Ive been bleeding for 12 days straight, it's not heavy barely filling one side of my tamp. Af was late by 4 days (started on the 17th) and now it won't stop. My cousin (who is a nurse) told me it could be from pregnancy but every test I take says negative. Could someone shine some light on what could be going on. I'm starting to get scared and worried